1. Field of the Invention
This invention relates to an ultravioletsetting resin composition which is applied to the formation of a thin resin setting layer such as paint, printing ink and bonding agent and increasingly applied presently in particular to the formation of a thick resin setting layer such as potting for electronic parts.
2. The Prior Art
In a prior art related to this invention, the thick ultravioletsetting resin which usually contains urethanemodified acrylate is soft and consequently vulnerable to scratches.
Japanese Examined Published Patent Application No. 37322/1983 under the title of "Ultravioletsetting Resin Composition" publicizes a means for eliminating such imperfections. This Japanese application discloses a means for raising the permeability to ultraviolet rays, shortening the setting time and increases the surface hardness by adding glass beads of 60 to 850 .mu.m in particle size (hereinafter referred to as "Glass Beads") to the ultravioletsetting resin.
The ultraviolet resin is well known and described in such papers: (1) S. Peter Pappas: UV Curing, science and Technology, p. 161 Technology Marketing Corporation, (1978); (2) Celanese Chemical Co., Technical Buletins, (1978), (1979).
In the process described above, however, if the Glass Beads of 60 .mu.m or more in particle size are added to the ultravioletsetting resin (hereinafter referred to "Resin"), these Glass Beads will sediment quickly in several hours due to the low viscosity of the Resin for potting. This leaves a small distribution of the Glass Beads in the surface area of the Resin when it is hardened by being subject to ultraviolet rays. As a result the surface hardness of the Resin is degraded and consequently it becomes vulnerable to scratches according as the degradation.
If the Glass Beads of under 60 .mu.m in particle size are added to the resin, the permeability to ultraviolet rays is degraded, the hardening of the Resin is consequently slowed and as a result the thick resin setting layer requires long time to be hardened.
Therefore, the object of this invention is to provide the resin whose surface becomes hard in a short time when ultraviolet rays are applied thereto in the above process.